Dresden Files Baltimore/D.C.
[[Magic in D.C.]]
The city’s design, with all it’s strange traffic circles and diagonal streets, was set up as a giant sigil. When wizards (or anyone) throws large amounts of magical power around, the power is ground out and absorbed into the city. That power is funneled into magical circuits that keep the sigil running. Excess is channeled deeper, and seems to be fueling some other Working. The While Counsel claims not to know the exact nature of this working. Most wizards avoid the area because they don’t like their own magical projects being drained of power in order to fuel an unknown project.
The sigil doesn’t seem to cancel out faith magic, and Jefferson’s agreement with the Faerie Queens keeps Fae magic from being a big issue.